1. The word pero is usually the equivalent to the English conjunction but however, there is also sino that means but that is used after a negative in order to offer the idea of an alternative: not this, but rather that
No voy a beber jugo de frutas sino agua
2. You can also use sino with no sólo... sino también... (not only,,, but also)
Apareció no sólo la luna sino también el sol
3. You use sino que instead of sino when there is a conjugated verb in the second part of the sentence
No vendí mis libros sino que los regalé